Not only there needs to be a reject option, but it must be the same size, weight and color so as not to influence the decision of the user. And be truthful, in most cases there should not be a banner at all: 99% of websites don't need cookies and when you do they're covered by other areas of GDPR (such as providing a requested service) which don't need explicit consent.

In all cases where you see a banner for accepting cookies, the company behind it is doing something nasty to the users. (i have yet to see a counter-example to that)